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From: Joey Pabalinas <joeypabalinas@gmail.com>
To: Qian Cai <cai@lca.pw>
Cc: akpm@linux-foundation.org, esploit@protonmail.ch,
	jejb@linux.ibm.com, dgilbert@interlog.com,
	martin.petersen@oracle.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	Joey Pabalinas <joeypabalinas@gmail.com>
Subject: Re: [PATCH] rbtree: fix the red root
Date: Fri, 11 Jan 2019 07:17:43 -1000
Message-ID: <20190111171743.qx44dlsdaowdt3no@gmail.com> (raw)
In-Reply-To: <20190111165145.23628-1-cai@lca.pw>

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On Fri, Jan 11, 2019 at 11:51:45AM -0500, Qian Cai wrote:
> A GFP was reported,
> 
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
>         kasan_die_handler.cold.22+0x11/0x31
>         notifier_call_chain+0x17b/0x390
>         atomic_notifier_call_chain+0xa7/0x1b0
>         notify_die+0x1be/0x2e0
>         do_general_protection+0x13e/0x330
>         general_protection+0x1e/0x30
>         rb_insert_color+0x189/0x1480
>         create_object+0x785/0xca0
>         kmemleak_alloc+0x2f/0x50
>         kmem_cache_alloc+0x1b9/0x3c0
>         getname_flags+0xdb/0x5d0
>         getname+0x1e/0x20
>         do_sys_open+0x3a1/0x7d0
>         __x64_sys_open+0x7e/0xc0
>         do_syscall_64+0x1b3/0x820
>         entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> It turned out,
> 
> gparent = rb_red_parent(parent);
> tmp = gparent->rb_right; <-- GFP triggered here.
> 
> Apparently, "gparent" is NULL which indicates "parent" is rbtree's root
> which is red. Otherwise, it will be treated properly a few lines above.

Good catch, acked. After thinking through the logic a bit your solution
seems like the simplest fix.

Now, I didn't do _extensive_ testing but a quick compile and bootup of
the patch with CONFIG_KASAN_INLINE enabled has yet to throw any GFPs,
so take that as you will.

Reviewed-by: Joey Pabalinas <joeypabalinas@gmail.com>
Tested-by: Joey Pabalinas <joeypabalinas@gmail.com>

> /*
>  * If there is a black parent, we are done.
>  * Otherwise, take some corrective action as,
>  * per 4), we don't want a red root or two
>  * consecutive red nodes.
>  */
> if(rb_is_black(parent))
> 	break;
> 
> Hence, it violates the rule #1 and need a fix up.
> 
> Reported-by: Esme <esploit@protonmail.ch>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  lib/rbtree.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/lib/rbtree.c b/lib/rbtree.c
> index d3ff682fd4b8..acc969ad8de9 100644
> --- a/lib/rbtree.c
> +++ b/lib/rbtree.c
> @@ -127,6 +127,13 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
>  			break;
>  
>  		gparent = rb_red_parent(parent);
> +		if (unlikely(!gparent)) {
> +			/*
> +			 * The root is red so correct it.
> +			 */
> +			rb_set_parent_color(parent, NULL, RB_BLACK);
> +			break;
> +		}
>  
>  		tmp = gparent->rb_right;
>  		if (parent != tmp) {	/* parent == gparent->rb_left */
> -- 
> 2.17.2 (Apple Git-113)
> 

-- 
Cheers,
Joey Pabalinas

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  reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <YrcPMrGmYbPe_xgNEV6Q0jqc5XuPYmL2AFSyeNmg1gW531bgZnBGfEUK5_ktqDBaNW37b-NP2VXvlliM7_PsBRhSfB649MaW1Ne7zT9lHc=@protonmail.ch>
2019-01-11 16:51 ` Qian Cai
2019-01-11 17:17   ` Joey Pabalinas [this message]
2019-01-11 17:31   ` Matthew Wilcox
2019-01-11 17:53     ` Joey Pabalinas
2019-01-11 18:12     ` Qian Cai
2019-01-11 18:16       ` Matthew Wilcox
2019-01-11 20:58         ` [PATCH v2] " Qian Cai
2019-01-11 23:16           ` Matthew Wilcox
2019-01-12  0:18             ` Qian Cai
2019-01-12  0:39               ` Esme
2019-01-11 23:47           ` David Lechner
2019-01-12  2:58             ` Michel Lespinasse
2019-01-14  2:20               ` David Lechner
2019-01-14  2:33                 ` Qian Cai
2019-01-14  3:07                   ` Esme
2019-01-14  3:52                     ` Douglas Gilbert
2019-01-14  3:59                       ` Esme
2019-01-14  4:52                         ` Douglas Gilbert
2019-01-14  6:23                           ` Esme
2019-01-14 15:45                             ` Qian Cai
2019-01-14 15:51                               ` Esme
2019-01-14 17:58                                 ` Qian Cai
2019-01-14 18:26                                   ` Douglas Gilbert
2019-01-15  5:31                             ` Qian Cai
2019-01-16 14:37                               ` Esme
2019-01-18 17:10                                 ` Qian Cai

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